Tetsu Miyamoto

Energy Transfer to Gas-Puff Z-Pinch and X-Ray Radiation

Gas-puff z-pinch plasmas were generated using rare gases (Ne, Ar and Kr). The intensities of XUV and X-ray radiations increased with atomic number Z of the gas. The net energy transferred to the plasma also increased with Z of the gas, which is a direct result of strong radial compression of the plasma column. Multiple ionization plays an important role in the strong compression of the high Z z-pinch plasma.

Operating Regions of a Gas-Puff Z-Pinch and Its X-Ray Radiation

A z-pinch experiment is carried out with a hollow-shaped Ar gas puff. Three types of discharge are found depending on the delay time of discharge from gas-puff detection, and the pinch time is compared with the measured gas pressure profile. Strong X-ray radiation is emitted from spots, a cloud and the anode surface. The number of spikes in the X-ray signal is correlated with spot images of the X-ray photograph. An X-ray burst is sometimes observed in the short-delay-time operation.

Macroscopic Behavior and X‐ray Radiation Characteristics of SHOTGUN Z‐Pinch Plasma

Gas‐puff z‐pinch plasmas were produced using Ne, Ar, Kr and Xe as pinch materials in the SHOTGUN device. The hardening of x‐ray radiation with atomic number Z of the operating gas was confirmed. It results from higher energy input into the higher Z plasma due to stronger compression, which is attributed to radiation cooling in the contraction phase.The contracting plasma showed nonuniformity along the axis, which results from m = 0 unstable mode. As the nonuniformity develops, the plasma column is divided into several sections, and each of them collapses by turns from the anode. The x‐ray is emitted at several localized spots which corresponds to the nodes of the rippling.

Z‐pinch research at Nihon University

Descriptions of the following theoretical and experimental studies are given. First, the snowplow energy equation is derived and compared with the snowplow momentum equation, which has been used to investigate implosion processes. Second, the quasi‐steady processes are studied without assumption of perfect relaxation between electrons and ions. Third, the limitation of the line density for the Bennett pinch and the existence of ion‐current‐rich pinch is shown. Lastly, the results for a gas‐puff Z‐pinch with a strong density gradient and density minimum between electrodes are given.

Steady State of Dense Sheet Z-Pinch with Thermal Conduction

The problem of steady state of the sheet Z-pinch was solved, incorporating the thermal conductivity effects. Particularly, the classes of solutions with small plasma pressure and low temperature on the sheet boundary are investigated. There are 3 types of the temperature profiles. Dependence on the pinch plasma parameters is found.

Control of x-ray spectrum emitted from a gas-puff Z-pinch

The axial magnetic field is applied to an annular gas-puff z-pinch for the control of radial dynamics and x-ray emission from the pinched plasma. K-shell and L-shell radiations of Ar ions are detected separately, and only the K-shell radiation is suppressed significantly by the axial field. The radial motion of the plasma is analyzed assuming a simple circuit model. The characteristic radius of the plasma increased with increasing the axial field.

Corona-Triggering Surface Discharge Switch

Several improvements on surface discharge switch were investigated. A new triggering method based on both corona discharge and field distortion was demonstrated to be more reliable and better than for that based on only the field distortion or multiple pin triggers. It was shown that optimum values, at which the switch impedance decreased without losing the features of the surface discharge switch, existed for the thickness and width of the electrodes. The effects of floating electrodes were also investigated to decrease further the switch impedance. The damage to the discharge surface was substancially reduced remarkably by decreasing the switch resistance.

Quasi-steady processes of a high current Z-pinch

Abstract Quasi-steady states of an isolated high current Z-pinch are investigated analytically using two-temperature equations averaged in space. Some characteristic processes — a steady compression process etc. — are given. A new explanation for the results of the laser initiated gas-embedded Z-pinch experiments is also given.

Z pinches in a hollow gas cylinder

Abstract The fusion approach based on the use of strongly unstable plasma state is proposed. In the system, the unstable, hot plasma is produced repeatedly by Z pinches in a gas vortex with a high density gradient and in a surface magnetic field, and consists of three components — hot dense plasma clouds, energetic ions and a background plasma. The conditions needed to yield a net fusion gain are investigated.